Compositions and methods for CMP of the surface of a substrate are well known in the art. Polishing compositions (also known as polishing slurries, CMP slurries, and CMP compositions) for CMP of surfaces of semiconductor substrates (e.g., for integrated circuit manufacture) typically contain an abrasive, various additive compounds, and the like. Compositions for polishing nickel phosphorus (NiP) surfaces in rigid disk (hard drive) manufacture are known in the art. Such compositions typically utilize a silica or alumina abrasive, a primary oxidizing agent (e.g., hydrogen peroxide) and a secondary oxidizing agent (e.g., ferric ion).
In conventional CMP techniques, a substrate carrier or polishing head is mounted on a carrier assembly and positioned in contact: with a polishing pad in a CMP apparatus. The carrier assembly provides a controllable pressure to the substrate, urging the substrate against the polishing pad. The pad and carrier, with its attached substrate, are moved relative to one another. The relative movement of the pad and substrate serves to abrade the surface of the substrate to remove a portion of the material from the substrate surface, thereby polishing the substrate. The polishing of the substrate surface typically is further aided by the chemical activity of the polishing composition (e.g., by oxidizing agents, acids, bases, or other additives present in the CMP composition) and/or the mechanical activity of an abrasive suspended in the polishing composition. Typical abrasive materials include silicon dioxide, cerium oxide, aluminum oxide, zirconium oxide, and tin oxide.
U.S. Pat. No. 6,015,506 discloses a polishing composition including silica or alumina, an oxidizer (either H2O2 or potassium peroxymonosulfate) and a metal catalyst such as ferric nitrate in water solution at pH 2 to 7. This patent speculates that the use of additives such as phosphoric acid or an organic acid may reduce the oxidizer decomposition rate, but also may adversely affect the NiP removal rate. U.S. Pat. No. 6,280,490 discloses a polishing composition including an abrasive such as silica or alumina, a peroxydisulfate-based oxidizer and a ferric salt such as ferric nitrate, ferric sulfate or a ferric complex salt such as iron (III) citrate and iron (III) EDTA in water at pH 2 and greater. However, there is no teaching regarding the oxidizer and removal rate stability. The slurries of U.S. Pat. No. 6,280,490 that contained complexed iron salts afforded lower removal rates than those with non-complexed iron salts, although the comparison was made at different pH values. U.S. Pat. No. 6,309,434 discloses a polishing composition including silica as the abrasive, H2O2 as the oxidizer, ferric nitrate as a “polishing accelerator” and citric acid as a stabilizer, at a pH of greater than 2. U.S. Pat. No. 6,309,434 asserts that citric acid has an advantageous stabilizing effect compared to other stabilizers such as oxalic acid and malonic acid; however, this conclusion was based on results obtained without pH adjustment for different stabilizers for comparison at the same pH.
In order to improve manufacturing throughput for cost of ownership (CoO) reduction, high removal rate continues to be one of the top requirements for a first step NiP CMP slurry in the hard disk industry. Addition of ferric salts such as ferric nitrate in CMP slurry composition are known to improve removal rates due to the catalytic effect of the Fe3+ ion on NiP oxidation when combined with primary oxidizers such as hydrogen peroxide and persulfate salts. However, the presence of ferric ion can cause fast decomposition of peroxy-based oxidizers and therefore result in unstable compositions and erratic polishing performance. While chelating agents (chelators) with high ferric ion binding constants, such as ethylenediaminetetraacetic acid (EDTA) and N-(hydroxyethyl)ethylenediaminetriacetic acid (HEDTA), may help to significantly inhibit the rapid catalytic decomposition of peroxy-oxidizers, such chelators typically reduce the polishing removal rates at the same time. As a consequence, there is an ongoing need for compositions and methods that can improve oxidizer stability without significantly compromising NIP material removal rates for ferric ion-catalyzed CMP slurries. The compositions and methods described herein addresses this need.